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// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef MOJO_EDK_SYSTEM_WAITER_H_
#define MOJO_EDK_SYSTEM_WAITER_H_
#include <stdint.h>
#include "base/macros.h"
#include "base/synchronization/condition_variable.h"
#include "base/synchronization/lock.h"
#include "mojo/edk/system/awakable.h"
#include "mojo/edk/system/system_impl_export.h"
#include "mojo/public/c/system/types.h"
namespace mojo {
namespace edk {
// IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
// under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
// must never call out to other objects (in particular, |Dispatcher|s). This
// class is thread-safe.
class MOJO_SYSTEM_IMPL_EXPORT Waiter final : public Awakable {
public:
Waiter();
~Waiter();
// A |Waiter| can be used multiple times; |Init()| should be called before
// each time it's used.
void Init();
// Waits until a suitable |Awake()| is called. (|context| may be null, in
// which case, obviously no context is ever returned.)
// Returns:
// - The result given to the first call to |Awake()| (possibly before this
// call to |Wait()|); in this case, |*context| is set to the value passed
// to that call to |Awake()|.
// - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded; in this
// case |*context| is not modified.
//
// Usually, the context passed to |Awake()| will be the value passed to
// |Dispatcher::AddAwakable()|, which is usually the index to the array of
// handles passed to |MojoWaitMany()| (or 0 for |MojoWait()|).
//
// Typical |Awake()| results are:
// - |MOJO_RESULT_OK| if one of the flags passed to
// |MojoWait()|/|MojoWaitMany()| (hence |Dispatcher::AddAwakable()|) was
// satisfied;
// - |MOJO_RESULT_CANCELLED| if a handle (on which
// |MojoWait()|/|MojoWaitMany()| was called) was closed (hence the
// dispatcher closed); and
// - |MOJO_RESULT_FAILED_PRECONDITION| if one of the set of flags passed to
// |MojoWait()|/|MojoWaitMany()| cannot or can no longer be satisfied by
// the corresponding handle (e.g., if the other end of a message or data
// pipe is closed).
MojoResult Wait(MojoDeadline deadline, uintptr_t* context);
// Wake the waiter up with the given result and context (or no-op if it's been
// woken up already).
bool Awake(MojoResult result, uintptr_t context) override;
private:
base::ConditionVariable cv_; // Associated to |lock_|.
base::Lock lock_; // Protects the following members.
#ifndef NDEBUG
bool initialized_;
#endif
bool awoken_;
MojoResult awake_result_;
uintptr_t awake_context_;
DISALLOW_COPY_AND_ASSIGN(Waiter);
};
} // namespace edk
} // namespace mojo
#endif // MOJO_EDK_SYSTEM_WAITER_H_
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